System and method for improved leach stockpile drainage

ABSTRACT

Systems and methods for improving leach solution drainage in a stockpile leach operation are provided. In various embodiments, methods are provided comprising placement of a drainage measure or a system of drainage measures in a leach stockpile to improve leach solution flow through the stockpile. A system for recovery of metal values from a leach stockpile comprising a leach stockpile, a leach solution, a leach solution delivery system, a leach solution drainage system, and a leach solution recovery system are also provided.

FIELD

The present disclosure relates generally to systems and methods for recovery of leach solution from leach stockpiles. More particularly, the disclosure relates to systems and methods for enhancing recovery of metal-bearing leach solution from a leach stockpile, thereby increasing the efficiency of metal value recovery from a leach stockpile while also increasing the geotechnical stability of the leach stockpile.

BACKGROUND

Hydrometallurgical treatment of metal-bearing materials, such as metal ores, metal-bearing concentrates, and other metal-bearing substances, has been well established for many years. Moreover, leaching of metal-bearing materials is a fundamental process utilized to extract metals from metal-bearing materials such as copper-containing ores. In general, a leaching process consists of crushing, agglomeration, and stacking of the ore material in a leach stockpile or “heap,” followed by leaching of the ore in the heap with an aqueous solution, collection of a metal-bearing or “pregnant” leach solution (“PLS”), and recovery of dissolved metal values from the PLS to produce a saleable metal product.

The first step in a typical leaching process, such as a copper metal recovery process, is crushing mined copper mineral ore to reduce the rock particle size and expose copper mineralization while maintaining a size distribution that will provide acceptable percolation of solution through the ore that is stacked in a leach stockpile. For example, during the crushing step, ore may be crushed so that 80 percent of the particles are less than ¾-inch in size. A significant amount of fine material may also be generated in the crushing process. The crushed ore may then be delivered to feed an agglomeration step. Crushed ore is fed into agglomeration drums, where it may be mixed with water and sulfuric acid. The agglomeration step may provide a relatively uniform ore particle size distribution in the ore sent to the ore stockpile for leaching. Agglomerated ore is transported to the leach pad, for example, by a conveyor system, for stacking in the leach stockpile or heap. The final conveyor in the system may be, for example, a bridge-type mobile stacker or a radial stacker. The agglomerated ore is stacked in layers referred to as “lifts.” Each lift generally has a substantially uniform depth and may be several meters thick.

The leach pad on which the ore is stockpiled may comprise, for example, a compacted, low permeability base. This base is generally overlayed with a synthetic, impermeable liner on which a highly permeable drainage layer is placed. The drainage layer may include a PLS collection system to collect pregnant leach solution flowing out of the bottom of the leach stockpile. As described above, agglomerated ore is placed on this drainage layer in a series of lifts, and a stockpile of agglomerated ore (i.e., a “heap”) can comprise numerous lifts and tens to hundreds of meters of stacked material.

After a lift has been placed or section of a leach stockpile has reached a planned height, a leach solution distribution system may be placed on the top surface of the stockpile or beneath the surface. Leach solution is applied at or near the top of a lift or stockpile through leach solution delivery system, such as an irrigation system consisting of a network of sprinklers or emitters configured to apply leach solution uniformly across the heap. Leach solution flows downward through the material in the stockpile under the influence of gravity, reacting with the minerals in the ore to dissolve and liberate metal values from the ore it contacts.

Often, it is desirable that the void spaces between particles in the heap do not completely fill with leach solution, as air may be required for reaction of the lixiviant in the leach solution with the minerals in the ore. Instead, the application rate of the leach solution is controlled so that leach solution flows over and around the ore particles in a thin film that does not saturate the material. Control of the moisture content of the stockpile material thus affects leach process efficiency as well as the geotechnical stability of the leach stockpile.

However, a number of factors can affect the rate of transport of leach solution through the heap, including the application rate, moisture content of the ore, material characteristics of the material (fines content, clay content, etc.) the porosity or volume of void spaces in the material, densification, solution viscosity, and capillary forces. Despite adoption of well-defined operating practices during the crushing, agglomeration, and stacking steps of a leaching process to maintain heap permeability and uniform leach solution flow through the heap, the heap may not form a completely homogenous blend of ore material with consistent characteristics, and factors such as those listed above that can influence leaching performance may vary widely within a heap.

Variability of ore particle size degradation, densification, variable clay content and swelling, mechanical compaction, and other factors within the heap may produce localized areas of low solution permeability. Similarly, low solution permeability interfaces may form between lifts. Factors such as these can restrict the vertical transport of leach solution through the heap and cause localized zones of saturation. If an area becomes highly impermeable, it can restrict the downward flow of solution significantly, hindering further leaching from taking place in the ore below and adversely affecting metal value recovery. It also forces leach solution to find an alternative path to reach the bottom of the heap. This can lead to, for example, areas of high solution content near the edges of the heap, creating zones of geotechnical instability and other safety hazards.

Accordingly, methods and systems for improving leach solution flow through a leach stockpile are desirable.

SUMMARY

The present disclosure relates generally to systems and methods for improving the drainage of leach solution through a leach stockpile in a heap leach operation. In various embodiments, recovery of metal-bearing leach solution from a leach stockpile is improved by providing leach stockpile drainage measure systems and methods that enhance leach solution flow through a leach stockpile.

In various embodiments, a method for improving the drainage of leach solution through a leach stockpile comprises identifying a zone of low solution permeability in a leach stockpile and placing a drainage measure in the zone of low solution permeability. The drainage measure may comprise a proximal terminus and a distal terminus, and be disposed to place the proximal terminus on a first side of the zone of low solution permeability and the distal terminus on an opposite side of the zone.

In various other embodiments, a process for producing enhanced leach solution drainage in a leach stockpile may comprise delivering a leach solution to a leach stockpile with a leach solution delivery system, applying the leach solution to at least a portion of the leach stockpile, and installing a drainage measure in the leach stockpile. The drainage measure may be selected from a group consisting of wick drains, pipe drains, perforated drains, sheet drains, strip drains, chimney drains, combination drains, drain holes, and pumps. In accordance with various embodiments, the drainage measure is physically separate from the leach solution delivery system and a leach solution collection system.

In various embodiments, a system for recovery of metal values from a leach stockpile is provided. A system may comprise a leach stockpile comprising a plurality of stockpile lifts, a leach solution, and a leach solution delivery system. A leach solution delivery system may be coupled to the leach solution and configured to deliver leach solution to the leach stockpile. A system may comprise a leach solution drainage system disposed in the leach stockpile and configured to facilitate leach solution transfer across zones of decrease leach solution permeability. A system may also comprise a leach solution collection system disposed at the bottom of the leach stockpile and configured to collect pregnant leach solution flowing out of the leach stockpile.

As set forth in more detail below, various advantages of the systems and methods of the present disclosure include improved leach solution flow through a leach stockpile, improved leach solution and metal value recovery, and/or enhanced geotechnical stability and safety of a heap leach operation.

Further areas of applicability will become apparent from the detailed description provided herein. It should be understood that the description and specific examples are intended for purposes of illustration only and are not intended to limit the scope of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS

The subject matter of the present disclosure is particularly pointed out and distinctly claimed in the concluding portion of the specification. A more complete understanding of the present invention, however, may best be obtained by referring to the detailed description when considered in connection with the drawing figures, wherein like numerals denote like elements and wherein:

FIG. 1 illustrates a flow diagram of a leach process comprising leach solution drainage measure placement in accordance with various embodiments;

FIGS. 2A-2C illustrate flow diagrams of leach processes comprising placement of a drainage measure system in accordance with various embodiments;

FIG. 3 illustrates a leach stockpile with leach solution drainage measures in accordance with various embodiments;

FIG. 4 illustrates a system for recovery of metal values from a leach stockpile in accordance with various embodiments; and

FIGS. 5A and 5B illustrate wick drains in accordance with various embodiments.

DETAILED DESCRIPTION

The following description is merely exemplary in nature and is not intended to limit the present invention, its applications, or its uses. It should be understood that throughout the drawings, corresponding reference numerals indicate like or corresponding parts and features. The description of specific examples indicated in various embodiments of the present invention are intended for purposes of illustration only and are not intended to limit the scope of the invention disclosed herein. Moreover, recitation of multiple embodiments having stated features is not intended to exclude other embodiments having additional features or other embodiments incorporating different combinations of the stated features.

Furthermore, the detailed description of various embodiments herein makes reference to the accompanying drawing figures, which show various embodiments by way of illustration. While the embodiments are described in sufficient detail to enable those skilled in the art to practice the invention, it should be understood that other embodiments may be realized and that logical and mechanical changes may be made without departing from the spirit and scope of the present invention. Thus, the detailed description herein is presented for purposes of illustration only and not of limitation. For example, steps or functions recited in descriptions any method, system, or process, may be executed in any order and are not limited to the order presented. Moreover, any of the step or functions thereof may be outsourced to or performed by one or more third parties. Furthermore, any reference to singular includes plural embodiments, and any reference to more than one component may include a singular embodiment.

The present disclosure relates generally to systems and methods for recovering metal values from metal-bearing materials, and more specifically, to systems and methods for recovery of metal-bearing leach solution from a leach stockpile. As set forth in more detail below, various embodiments provide advancements over prior art processes, particularly with regard to metal-bearing leach solution recovery and process efficiency. Moreover, existing heap or ore stockpile leach processes that utilize a reactive process comprising contacting a metal-bearing material with a leach solution or lixiviant by gravity flow through an ore stockpile for metal value recovery may, in many instances, be easily retrofitted to exploit the many commercial benefits disclosed herein.

With reference to FIG. 1, a process of metal value recovery 100 is illustrated. Metal value recovery 100 may comprise identification of a zone of saturation and/or low solution permeability in a leach stockpile and placement of a drainage measure in the leach stockpile, as described in greater detail below.

In accordance with various embodiments of the present disclosure, a process of metal value recovery 100 comprises preparing the metal bearing material 10. Preparing a metal-bearing material 10 can comprise crushing or otherwise reducing the particle size of metal-bearing material. Metal-bearing material 101 may be an ore at any stage of processing, a combination of ores, a concentrate, a process residue, a flotation tailings product, an impure metal salt, combinations thereof, or any other material from which valuable and/or useful metal values may be recovered. In various embodiments, metal-bearing material may be run-of-mine ore mined from an open pit. Metal-bearing material may also be ore obtained using any other mining or extraction process. As used herein, the terms “ore,” “fine ore,” and various alternatives thereof may be used interchangeably with the term “metal-bearing material.”

By way of specific example, metal value recovery 100 may be configured to recover copper from copper-bearing material, such as, for example, ores and/or concentrates containing chalcopyrite (CuFeS₂), chalcocite (Cu₂S), bornite (Cu₅FeS₄), and covellite (CuS), malachite (Cu₂CO₃(OH)₂), pseudomalachite (Cu₅[(OH)₂PO₄]₂), azurite (Cu₃(CO₃)₂(OH)₂), chrysocolla ((Cu,Al)₂H₂Si₂O₅(OH)₄.nH₂0), cuprite (Cu₂O), brochantite (CuSO₄.3Cu(OH)₂), atacamite (Cu₂[OH₃Cl]) and other copper-bearing minerals or materials and mixtures thereof.

In accordance with various embodiments, metal value recovery 100 may be configured to recover any of a variety of metals from a suitable metal-bearing material 101, and the copper-bearing minerals listed above are presented as examples, and not by way of limitation. Such metal values may include, for example, copper, gold, silver, zinc, platinum group metals, nickel, cobalt, molybdenum, rhenium, uranium, rare earth metals, and the like.

During preparation of metal-bearing material 10, metal-bearing material 101 is prepared for leaching process 20. Metal-bearing material 101 may be prepared in any manner that facilitates the recovery of metal values from metal-bearing material 101—such as, for example, manipulating a composition and/or component concentration of metal-bearing material 101—for leaching process 20. Desired composition and component concentration parameters can be achieved through a variety of chemical and/or physical processing stages, the choice of which will depend upon the operating parameters of the chosen processing scheme, equipment cost and material specifications. For example, metal-bearing material 101 may undergo agglomeration, comminution, flotation, blending, slurry formation, and any other chemical and/or physical conditioning in preparation of metal-bearing material 10 before a leaching process step. Leaching process 20 (i.e., extraction of metal values from the metal-bearing material) may begin to occur during the preparation of the metal-bearing material, depending on the nature of the physical and/or chemical processing stages used during the preparation of the material. Any processing of metal-bearing material 101 which improves the ability to recover metal values from the material is in within the scope of the present disclosure.

In various embodiments, preparation of metal-bearing material 10 comprises crushing of ore containing metal values. Crushing may be used to reduce the size of the ore particles, for example, to expose copper mineralization, while maintaining a resulting particle size distribution that provides desired performance parameters during reactive processing, such as acceptable flow of leach solution through a stockpile of the prepared metal-bearing material. In various embodiments, the particle size of metal-bearing materials may be reduced using a crusher, or, for example, a series of crushers arranged in a crushing circuit. A crushing circuit may comprise a plurality of crushers and/or screening facilities that may be used to sequentially reduce the particle size of the ore and separate ore that has been reduced within the desired size range from ore requiring further crushing. In various embodiments, preparation of metal-bearing material 10 may produce a fine ore comprising 80 percent of the material ¾-inch in size or smaller. This fine ore may further comprise very fine or powdered ore material, referred to as “fines”, which is defined as that portion of the material smaller than 75 microns in diameter.

Other methods of preparing a metal-bearing material, such as controlled grinding, may also be used to produce a uniform particle size distribution of metal-bearing material 101 in preparation of metal-bearing material 10. Additionally, liquid, such as process water, may be added to metal-bearing material 101 to create a pulp density which corresponds to desirable operating conditions of the controlled grinding unit. Various acceptable techniques and devices for reducing the particle size of the metal-bearing material include, for example, ball mills, tower mills, grinding mills, attrition mills, stirred mills, horizontal mills and the like, and additional techniques may later be developed and achieve the desired result of reducing the particle size of the metal-bearing material.

In various embodiments, preparation of metal-bearing material 10 may further comprise an agglomeration step. For example, reduced-size or fine ore from the crushing circuit may be delivered to a fine ore storage bin. The fine ore may in turn be fed to agglomeration drums. As the ore enters the agglomeration drums, it may be treated with a solution, such as a solution containing a lixiviant. For example, a copper-bearing ore may be treated with water and sulfuric acid in an agglomeration step. The drums rotate and mix the ore with the water and acid, and the tumbling action of the ore in the drums causes fines particles in the ore to adhere to coarser particles. This particle agglomeration provides for a relatively uniform size distribution of particles in the heap, which in turn may improve the leach solution permeability characteristics of the ore.

In accordance with various embodiments, agglomeration additives or agglomerating agents may be added to an ore in an agglomeration step. For example, in accordance with various embodiments, agglomerating agents such as cement, lime, sodium silicate, polymeric binders, and the like may be added to an ore in an agglomeration step to improve agglomeration. Agglomeration may be improved with respect to characteristics such as uniformity of particle size, particle strength, particle resistance to disintegration under various chemical or physical conditions, and the like. Any additive or agent, now known or hereinafter developed, that may be used in an agglomeration step to improve the formation of competent agglomerates and/or downstream leach process performance is within the scope of the present invention.

During agglomeration, sufficient liquid may be added to the ore to bring the moisture content of the ore within a range of from 0 to 20 percent. In various embodiments, the moisture content of the ore may be adjusted within a range of from 4 to 16 percent. In still other embodiments, the moisture content of the ore may be adjusted within a range of from 8 to 12 percent. For example, in accordance with various embodiments, water and/or acid may be added to a copper-containing ore in an agglomeration step to bring the moisture content of the ore to about 8 to 9 percent. The moisture content range to which the ore is adjusted during an agglomeration step may be dependent on, for example, the mineral composition and/or physical characteristics of the ore, addition of agglomerating agents, and the like.

Depending on the mineral composition of the ore, minerals in the ore may react with the water and acid added during agglomeration. Certain types of ore with various highly reactive minerals, such as calcite, may consume significant quantities of acid added during the agglomeration step. In accordance with various embodiments, the ore may be blended (before, during, or following crushing) to maintain a relatively consistent mineral composition, for example, to facilitate control of acid consumption during the agglomeration and enable initiation leaching of metal values from the ore during agglomeration.

In various embodiments, preparation of metal-bearing material 10 further comprises placing the metal-bearing material in a stockpile or “heap” for reactive processing by leaching process 20. In various embodiments, prepared metal-bearing material, such as agglomerated metal-bearing material exiting the agglomeration step, may be transported to a site at which the stockpile or heap is to be created and subjected to leaching process 20, also referred to as a “heap leach” operation or “heap leaching.” For example, and with reference also to heap leach operation 300 illustrated in FIG. 3, the prepared metal-bearing material may be transported to a leach pad 311 on which it is stacked for further processing by heap leaching. Prepared metal-bearing material may be transported, for example, by conveyor systems, trucks, loaders, or any other suitable method. Prepared metal-bearing material transported to the leach pad is then stacked on the leach pad in layers or “lifts” 312 that together form the leach stockpile 313. In various embodiments, the material is stacked by a stacking system configured to move across the leach pad and deposit relatively uniform layers of prepared ore. For example, in various embodiments, a radial stacker may be configured to deposit agglomerated ore in 15 to 30-foot high, rectangular lifts.

In accordance with various embodiments, a leach pad comprises a containment facility configured to contain the stacked ore, as well as collect and transport the solutions that are used and/or produced in the leaching process. For example, in cross-section from the bottom up, a leach pad 311 may be constructed of a compacted base of native soil, a 12-inch layer of low permeability compacted clay, a liner 314, such as a 60 or 80-mil synthetic liner of HDPE, a solution drainage system 315, such as a system of perforated HDPE pipe, and a screened rock drainage layer 316 that is highly permeable to leach solution and provides protection for both the liner system and drainage piping. The liner and drainage piping system may be further protected with a layer of run-of-mine material. Prepared ore is stacked on this rock drainage layer in lifts 312 by the conveyor stacking system, as described above. The leach pad may be built, for example, in the shape of a large rectangle; however, any suitable shape or configuration may be used. In various embodiments, when a single lift of has been placed across a leach pad area suitable for placement of a leach solution delivery system and leaching, it may be leached in a leaching process 20, described in greater detail below. Additional lifts may be placed on the heap, with the stacking system placing a second lift directly on top of the underlying ore layer which has completed a leach cycle. In various embodiments, multiple lifts may be placed on a heap prior to proceeding with a leaching process 20. Any possible logical order of lift placement in a leach stockpile and leaching of a lift in a leach process is within the scope of the present disclosure, including leach processes using “on-off” (i.e., reusable) leach pads in which lifts are removed after the leaching process is completed and the leached ore replaced with fresh ore.

In accordance with various embodiments, preparation of metal-bearing material 10 may further comprise manipulation of a lift following placement of the lift. For example, a bulldozer equipped with tines configured to penetrate the upper portion of a lift may be used to perform ripping of the top surface of a lift following lift placement and prior to proceeding with leaching process 20. In accordance with various embodiments, ripping or similar processes following lift placement may improve heap permeability by reducing formation of low permeability interfaces between lifts.

With reference to FIG. 1, following placement of a lift or completion of a section of a heap suitable for leaching, a metal value recovery process may further comprise leaching process 20. In accordance with various embodiments, leaching process 20 comprises a heap leach process. In various embodiments, a heap leach process comprises application of a leach solution to one or more lifts in a heap. In accordance with various embodiments and with continued reference to FIGS. 1 and 3, leach solution is applied to the top of a lift or the top of a heap with a leach solution delivery system 317. A leach solution delivery system may comprise a network of distribution piping and sprinklers or drip irrigation tubing comprising emitters laid out on the top surface of a lift or heap. As used herein, sprinklers, sprayers, drip irrigation emitters, or any other similar devices that may be used to transfer or apply leach solution from a fluid conduit to a lift or heap are collectively referred to as “emitters.” The leach solution delivery system may be configured so that emitters 318 are arranged at regular intervals across the top of the section of the lift or heap to be leached. In various embodiments, emitter spacing may be arranged based on parameters such as the measured or predicted hydraulic properties of the ore to be leached, the application rate of the leach solution through each emitter, or any other operational parameter that may be considered to optimize the leaching process 20 and metal value recovery from the material in the heap.

In accordance with various embodiments, leach solution may be applied to the top surface of a lift or heap using a leach solution delivery system comprising sprinklers, sprayers, or the like. In further embodiments, leach solution may be applied using a sub-surface delivery system, or leach solution may be applied using a combination of sub-surface and surface-located applicators. Any system that may be used to apply a leach solution to a heap in a uniform and controlled fashion is within the scope of the present disclosure.

As used herein, a leach solution may be an aqueous solution that comprises a lixiviant used to extract a metal value from the metal-bearing material in the heap. For example, in various embodiments, the leach solution may be an aqueous solution comprising sulfuric acid. In various embodiments, the leach solution may be an aqueous basic solution, for example, a basic solution comprising at least one of ammonia and ammonium, or comprising hydroxide and cyanide. The leach solution may be a fresh leach solution that has not previously been reacted with a metal-bearing material, or the leach solution may comprise a raffinate solution previously used in a reactive processing step for extraction of metal values. Recovery of dissolved metal values from a metal-bearing leach solution, for example, by a solution extraction process, can regenerate the lixiviant in the leach solution, producing a raffinate that may be recycled for use in further reactive processing. A raffinate may comprise other dissolved ions and metals, such as alumina, calcium, iron, magnesium, manganese, zinc, sulfate, cobalt, gold, silver, molybdenum, rhenium, residual copper, and various other metals and ions.

While not wishing to be bound by theory, it is believed that irrigation of a lift or heap with leach solution at a rate to produce a condition of “unsaturated flow” may be especially advantageous in certain heap leaching operations. In such operations, solution is applied to the top of the heap at a rate that allows solution to flow through the heap without reaching the point of saturation. As used herein, the term “saturated” means that the void spaces between ore particles in the heap or a portion thereof are filled with leach solution to the point that air flow and/or leach solution flow is restricted. As used here, the term “unsaturated” means that air or another gas is present in the void spaces and can flow in or through the void spaces. In accordance with various embodiments, in an “unsaturated flow” condition, air can flow or be transported to the surface of ore particles to participate as required in desired chemical reactions, such as reactions that liberate metal values from the ore particles. As described above, agglomerated ore placed in a heap may have a typical moisture content of 8 to 9 percent. In accordance with various embodiments, once the moisture content reaches approximately 8 to 12 percent, dependent on various parameters such as ore material physical characteristics, solution begins to flow downward through the heap under the influence of gravity. As used herein, “unsaturated flow” occurs when the void spaces between particles in the heap do not completely fill with leach solution; instead, the solution flows over and around the ore particles in a thin film that does not saturate the material. The presence of air within the heap may be required in certain types of leach operations for reaction of the lixiviant with the metal values in the ore; thus, saturation of the ore during leaching may hinder the reactive process required to liberate metal values from the metal-bearing material. Additionally, saturated conditions in the ore lift may cause geotechnical stability problems in the heap, channeling and uneven flow of leach solution through the heap, and other conditions that may further influence the efficiency as well as the safety of a heap leach operation.

In accordance with various embodiments, the downward flow or transport of leach solution through the lifts on the leach pad, illustrated in FIG. 3 as vertical dotted lines 319, is dependent almost entirely on gravity. A number of factors may affect the rate of transport of leach solution through the heap including, for example, the irrigation rate (i.e., the rate of application of leach solution), moisture content of the ore, material characteristics of the material (e.g., fines content, clay content, etc.) the porosity or volume of void spaces in the material, solution viscosity, and capillary forces.

Certain parameters such as those outlined above can be controlled during preparation of metal-bearing material 10 and leaching process 20. However, in accordance with various embodiments, zones of low solution permeability may be present in a leach stockpile. While not wishing to be bound by theory, it is believed that such zones may be formed during placement of the ore in the heap or over the course of reactive processing and/or addition of successive lifts to a heap. Although various operating parameters may be implemented during steps such as crushing, agglomeration, stacking, and ripping to facilitate production of a heap comprising a predicted or designed permeability to the leach solution to be used during leaching, a heap may not comprise a completely homogenous blend of one material type having uniform material characteristics. Factors described above that influence the rate of transport of leach solution through the heap may vary within the heap and/or change in a non-uniform manner within the heap in the course of the leaching operation. For example, certain ores may have a tendency to degrade into smaller particle sizes over the course of leaching and mechanical working of the ore. Fines produced as a result of chemical or mechanical degradation may migrate into void spaces in the heap and inhibit the permeability of a region of the heap to leach solution. Additionally, the increasing weight of the ore in the heap on lower lifts as new lifts are placed above may result in increased material density in portions of lower lifts. Similarly, mechanical compaction and physical decrepitation caused by equipment traffic on the surface of a lift before and/or during placement of an overlying lift may result in formation of relatively low permeability interfaces between lifts, for example, in the upper 1-3 meters of material in the underlying lift.

In various embodiments, metal value recovery 100 may comprise identification of a zone of saturation and/or low solution permeability 30 in a leach stockpile. In accordance with various embodiments, identification of a zone of saturation and/or low solution permeability 30 may be performed at various points in a heap leach operation, including prior to application of leach solution to the heap or during a leaching process. As used herein, the term “zone of saturation” is used to refer to an area of impounded or “perched” solution in the leach stockpile, such as an area in which leach solution has saturated the pores of an area the stockpile material, an area with an increased pore pressure, or an area otherwise reached a moisture level higher than would be expected under a condition of unsaturated flow. As used herein, the term “zone of low solution permeability” means a stratum, lens, or other region having any possible configuration in a heap that exhibits an increased resistance to percolation or flow of leach solution relative to the surrounding or adjacent material in the heap, or relative to the average or typical material in the heap. Similarly, as used herein, the term “zone of increased material density” means a stratum, lens, or other region having any possible configuration in a heap that exhibits a higher level of compaction or material density relative to the surrounding or adjacent material in the heap, or relative to the average or typical material in the heap. The terms “densification” or “zone of densification” may also be used to describe an increase in the density of material in a region of the heap.

In various embodiments, a zone of low solution permeability may be identified by identifying a zone of increased material density, and vice versa, and the two terms may be used interchangeably to describe functional aspects of a leach stockpile with respect to leach solution flow. Any now known or hereafter devised method of performing stratigraphic profiling and/or detection of a zone of increased material density in an ore stockpile may be utilized in accordance with various aspects of the present disclosure. For example, cone penetration testing may be used to determine the geotechnical properties of the heap in situ and to identify and/or delineate zones of low solution permeability or increased material density.

In various embodiments, a zone of low solution permeability may also be identified indirectly by identifying or locating a zone of increased moisture content or hydraulic pressure (i.e., a zone of saturation). The moisture content of heap material may be determined using any now known or hereafter devised laboratory or in situ method of measuring the moisture content of a material, including, for example, gravimetric or electrical resistivity measurement-based methods. By way of specific example, cone penetration testing with the use of a piezocone penetrometer may be used to determine pore water pressure of the heap in situ. In other embodiments, remote sensors may be placed in one or more locations in a heap to continuously or periodically monitor a measureable condition such as the moisture content of the material in the heap at the location of the sensor. The remote sensors may transmit data representing a measured condition to a receiving device configured to receive data from the remote sensors. The receiving device may be connected to a system such as a computer system configured to collect, record, and report data provided by remote sensors or other testing devices. Any method that may be used to measure or monitor the moisture content of the material in a heap is within the scope of the present disclosure.

In accordance with various embodiments, metal value recovery 100 may comprise placement of drainage measure 40 in a zone of saturation or a zone of low solution permeability. As used herein, the term “drainage measure” can comprise any device or structure that facilitates leach solution penetration into and/or flow through a zone of low solution permeability. In accordance with various embodiments, a drainage measure may comprise an elongated device having two ends, such as a proximal terminus and a distal terminus, although any suitable configuration is possible. As used herein, a “proximal terminus” can comprise an end of a drainage measure that leach solution may be expected to move away from following placement in a leach stockpile, and a “distal terminus” can comprise an end of a drainage measure that leach solution may be expected to flow toward. For example, where leach solution movement in or along the drainage measure is expected to be gravity-driven, a proximal terminus of the drainage measure may be at a higher elevation in the leach stockpile than the distal terminus following placement. In another example, where leach solution may be expected to move in or along a drainage measure by hydraulic pressure or capillary action, such as for a horizontally oriented drainage measure, the proximal terminus may be the end of the drainage measure located in or around a portion of the leach stockpile with a higher leach solution concentration, and the distal end located in or around a portion with a lower solution concentration.

In accordance with various embodiments, a drainage measure can comprise a wick drain (i.e., a vertical wick drain, band drain, or PVD drain), a sheet drain, a strip drain, a drain pipe, a perforated drain pipe, a chimney drain, a combination drain, a drain hole and/or pump, and the like. In various embodiments, a drainage measure, such as a wick drain or a sheet drain, does not comprise a pipe or other similar tubular configuration used for communication of a fluid. With reference to FIGS. 5A and 5B, wick drains 500A and 500B in accordance with various embodiments are illustrated. A wick drain or other non-tubular drain may comprise, for example, a formed three dimensional core (570A, 570B) such as a polypropylene strip fabricated with longitudinal open grooves or channels (571A, 571B). The core may be wrapped in a geotextile filter jacket 572, comprised, for example, of spunbond polypropylene or any other material and/or configuration that is highly water permeable while preventing fine particles from passing through the jacket. Drainage measures may comprise materials that have suitable chemical resistance to leach solution and other chemicals that may be used in a leach operation, as well as suitable mechanical strength and durability to withstand the physical and environmental challenges presented by placement and operation in a heap leach environment.

Drainage measures may be placed in a stockpile in any suitable configuration, such as vertically, horizontally, or in any other orientation. In accordance with various embodiments, the location in which a drainage measure is required and/or placed in a heap may influence the type of drainage measure that is selected and the configuration and orientation in which it is placed.

Placement of a drainage measure 40 in a zone of low solution permeability may comprise placing the drainage measure such that the proximal end is disposed on a first side of the zone of low solution permeability and the distal end is disposed on an opposite side. In accordance with various embodiments, following placement of drainage measure 40, the drainage measure may be disposed through the zone of low solution permeability, with the proximal end and the distal end of the drainage measure located in the leach stockpile on opposite sides of the zone in solution permeable areas. In other embodiments, an end, such as the distal end, may be disposed within the zone of low solution permeability. Any logical possible configuration of a drainage measure with respect to a zone of low solution permeability following placement of drainage measure 40 is within the scope of the present disclosure.

In accordance with various embodiments, placement of drainage measure 40 in a leach stockpile to which leach solution has been applied may result in a transfer of leach solution from the leach stockpile to the drainage measure. Leach solution transferred to the drainage measure may then be transported by the drainage measure from a first location to a second location. Leach solution transport in or along a drainage measure may result from gravity, pressure, capillary action, or any other force that may produce solution movement through or along a drainage measure. Leach solution transferred from the leach stockpile to the drainage measure may be transported by the drainage measure from a first area of the stockpile to a second area of the stockpile. For example, and as illustrated in FIG. 3, placement of one or more drainage measures 321 or 325 in a zone of low solution permeability 322A or a zone of increased material density 322B may enable leach solution 319 to flow through the zone of low solution permeability, such as from a first solution permeable area overlying the zone of low solution permeability to a second solution permeable area underlying the zone of low solution permeability. In accordance with various embodiments, placement of a drainage measure through a zone of low solution permeability 322A or increased material density 322B may result in transfer of leach solution through the zone of low solution permeability by the drainage measure and reduction of a hydraulic pressure in a portion of the leach stockpile, caused, for example, by an accumulation of leach solution in the leach stockpile in an area overlying the zone of low solution permeability.

In accordance with various embodiments, placement of drainage measure 40 in a zone of low solution permeability may permit leach solution to contact unleached or incompletely leached metal-bearing material 323. For example, metal-bearing material underlying a zone of low solution permeability may be incompletely leached due to poor leach solution penetration through the zone of low solution permeability. While not wishing to be bound by theory, it is believed that at least a portion of the leach solution flowing through a drainage measure such as a wick drain placed through a zone of low solution permeability may transfer from the wick drain to the ore in areas of solution-permeable material adjacent to the wick drain. Such transfer of leach solution through zones of low solution permeability to underlying metal-bearing material may produce increased metal-value recovery from previously unleached or incompletely leached material.

In various embodiments, placement of drainage measure 40 may comprise placement of a drainage measure, such as side slope drain 325, through a zone of saturation 324. A zone of saturation 324 may be identified using any suitable method, such as various methods described above. In various embodiments, a zone of saturation may be identified without identifying one or more zones of low solution permeability 322A or increased material density 322B that may be responsible for or have contributed to leach solution accumulation in the leach stockpile and creation of the zone of saturation.

Regardless of whether a zone of low solution permeability 322A or increased material density 322B is identified, one or more drainage measures may be placed through the zone of saturation 324 and into underlying or other adjacent areas within the leach stockpile. In various embodiments, a drainage measure such as a wick drain may be placed in and/or through a zone of saturation and extend continuously to another region of the leach stockpile, such as unsaturated area adjacent to the zone of saturation. For example, a drainage measure may be placed into and/or through a zone of saturation in a configuration that is substantially vertical or at an angle to vertical and extend continuously downward into the leach stockpile from the zone of saturation. Leach solution in the zone of saturation adjacent to the drainage measure may transfer to the drainage measure and flow along the drainage measure, for example, under the force of gravity and/or capillary action. In accordance with various embodiments, placement of a drainage measure into and through the zone of saturation decreases the hydraulic pressure of the leach solution in the zone of saturation in the region of the installed drainage measure. While not wishing to be bound by theory, it is believed that placement of a drainage measure through a zone of saturation and into non-saturated stockpile material located elsewhere in the stockpile along the length of the drainage measure may increase the recovery of leach solution from the leach stockpile and/or provide for increased leaching of incompletely leached material.

In various embodiments, placement of drainage measure 40 may comprise placement of a drainage measure in an interface between a first stockpile lift and a second stockpile lift. Placement of a drainage measure in a stockpile lift interface can comprise placement such that the drainage measure extends continuously through (i.e., traverses) the interface. In various embodiments, an interface between a first and a second lift may comprise a zone of increased material density (i.e., densification) 322B. Equipment traffic on the top surface of a lift may produce compaction of a stratum of lift material near the top surface of the lift (e.g., the first lift), such as the upper 1 to 3 meters of the lift. Such compaction may affect an entire lift, or a portion of the area of a lift. Placement of a second lift on top of the first results in an interface between the two lifts. A zone of increased material density located near the interface can comprise an area of compaction in the lower of the two lifts such as that described above. A zone of increased material density can also comprise fines and/or other small particles or particle degradation products that may migrate downward through the upper of the two lifts and accumulate in void spaces of a lower stratum of the upper lift, for example, due to a decreased rate of solution flow near the interface caused by compaction of an area of the top of the lower lift. The reduction in void space that may occur in the vicinity of an interface between lifts due to factor such as those described above can result in a zone of decrease leach solution permeability in the area of the interface or portions thereof. In various embodiments, placement of a drainage measure through the interface may increase the flow of leach solution through portions of an interface and into the underlying lift material and/or heap.

A zone of decreased leach solution permeability or a zone of saturation occurring near an edge of a stockpile can result in geotechnical instability within the stockpile such as a potential for side slope failure. For example, a zone of low solution permeability, such as zone of increased material density 322B, and resultant zone of saturation 324 near the edge of leach stockpile 313 may result in leach solution seeking an alternative flow path leading out of the edge of the heap, producing a “blowout” or stockpile material landslide on the stockpile side slope. Such an event can pose personnel and environmental safety hazards, as well as costs associated with decreased metal value recovery, leach operation efficiency, and remediation.

In various embodiments, placement of drainage measures in the leach stockpile may mitigate the potential for such an occurrence and provide for increased geotechnical stability of the leach stockpile. For example, drainage measures such as side slope drains 325 placed in a side slope of the leach stockpile and extending through the region located adjacent to the edge of the side slope and into the interior of the heap may provide for transfer of leach solution that may accumulate near the edge of the stockpile to lower, interior regions of the stockpile.

In accordance with various embodiments, a drainage measure placed in a leach stockpile during placement of drainage measure 40 is physically separate from (i.e., not physically connected to) the leach solution delivery system 317. As described above, a leach solution delivery system 317 is used to deliver and/or apply leach solution to a leach stockpile, and leach solution applied to the stockpile percolates through the stockpile material in the spaces between ore particles. Drainage measures such as drainage measure 321 and side slope drain 325 may receive leach solution 319 from the stockpile material in the vicinity of the drainage measure, such as in the manner described above. Drainage measures in accordance with various embodiments do not receive leach solution directly from a fluid distribution system. A drainage measure instead may facilitate movement of leach solution 319 that has entered the stockpile following application by the leach solution delivery system 317, transferring leach solution from a first area of the stockpile to a second area of the stockpile.

In accordance with various embodiments of metal value recovery 100, placement of drainage measure 40 is performed following application of leach solution to at least a portion of the leach stockpile. Thus, at least a portion of the leach stockpile is leached or partially leached prior to placement of a drainage measure in the stockpile, and placement of a drainage measure 40 may facilitate movement of metal-bearing or “pregnant” leach solution through the stockpile. In various other embodiments, drainage measures may be placed in a leach stockpile prior to application of leach solution to the stockpile. Application of leach solution to the leach stockpile and placement of drainage measures may proceed in any possible logical order in accordance with the present disclosure.

In various embodiments, metal value recovery 100 further comprises continued leaching and collection of pregnant leach solution 60 for metal value recovery, described in greater detail below.

With reference to FIGS. 2A-2C, processes for providing improved leach solution drainage 200A-200C in a leach stockpile in accordance with various embodiments are illustrated. Processes 200A-200C provide for placement of a drainage measure system in a leach stockpile during a leaching process and enhanced leach solution flow through the stockpile material. Processes 200A-200C may thereby provide enhanced metal value recovery from the stockpile material.

In accordance with various embodiments, process 200A comprises preparation of metal-bearing material 10, leaching process 20, identification of zone of saturation and/or low solution permeability 30, prioritized placement of drainage measure 240 in leach stockpile, placement of drainage measure system 250, and continued leaching and collection of pregnant leach solution 60 for metal value recovery.

Process 200A can comprise preparation of metal-bearing material 10 and leaching process 20 steps, as described above with reference to FIG. 1. Process 200A can further comprise an identification of zone of saturation and/or low solution permeability 30 in the leach stockpile, also described above.

In accordance with various embodiments, process 200 can comprise prioritized placement of drainage measure 240. In various embodiments, prioritized placement of drainage measure 240 may be performed as described above with respect to placement of drainage measure 40. Prioritized placement of drainage measure 240 may be performed following identification of zone of saturation and/or low solution permeability 230, also described above. In other embodiments, such as process 200B illustrated in FIG. 2B, prioritized placement of drainage measure 240 may be performed without performing prior identification of zone of saturation and/or low solution permeability 230. For example, prioritized placement of drainage measure 240 may be performed by placing drainage measures at sites in a leach stockpile known or suspected to have an increased likelihood of comprising a zone of saturation or low solution permeability based on, for example, the construction or configuration of the stockpile, the flow rate of leach solution recovered from a region of the stockpile, or the like.

Prioritized placement of drainage measure 240 may be performed, for example, at the outset of placement of drainage measure system 250 in the leach stockpile, described in greater detail below. Any process wherein, as an initial step of a method of systematic placement of drainage measures throughout a leach stockpile, one or more drainage measures are placed in the stockpile in regions known or suspected of having leach solution flow problems, is within the scope of the present disclosure.

In various embodiments and with reference to FIG. 2C, process for providing improved leach solution drainage 200C may not comprise identification of zone of saturation and/or low solution permeability 230 or prioritized placement of drainage measure 240. Process 200C may comprise preparation of metal-bearing material 10 and leaching process 20, followed by placement of drainage measure system 250, described below, and continued leaching and collection of PLS 60.

In accordance with various embodiments, processes 200A-200C comprise placement of drainage measure system 250 in the leach stockpile. Placement of drainage measure system 250 can comprise, for example, placing a plurality of wick drains in the leach stockpile. In various embodiments, a plurality of wick drains may be installed in the leach stockpile in a substantially vertical orientation and arranged in a predetermined configuration across all or a portion of the area of a leach stockpile. The pattern and/or spacing of the wick drains installed in the leach stockpile during processes 200A-200C may be determined based on, for example, the hydraulic properties of the stockpile material, the specifications and/or performance of the wick drains, the configuration of the heap, the leach solution flow through the heap, or any other property or combination of properties of the drainage measures, the stockpile material, the stockpile configuration, leach operation parameters, etc. In various embodiments, installation of a drainage measure system 250 can comprise placing any system of drainage measures in a leach stockpile. Examples of various systems of drainage measure systems that may be installed in a leach stockpile in processes 200A-200C are described in greater detail below.

In accordance with various embodiments, a system for recovery of metal values from a leach stockpile is also provided. In various embodiments and with reference now to FIG. 4, a system 400 for recovery of metal values from a leach stockpile may comprise a leach stockpile, a leach solution, a leach solution delivery system coupled to the leach solution, a leach solution drainage measure system, and a PLS collection system. A leach stockpile 413 in accordance with various embodiments may comprise a plurality of lifts 412, as described elsewhere herein. Leach solution 419 may be delivered to the leach stockpile by a leach solution delivery system 417 coupled to the leach solution at a source such as a leach solution or low grade raffinate storage tank or pond and configured to deliver the leach solution to the leach stockpile 413. In various embodiments, the leach solution delivery system 417 may deliver the leach solution 419 to the top surface of a lift or the leach stockpile, for example, using a network of emitters 418 that apply leach solution evenly across the top surface of the lift or stockpile. Alternatively, a leach solution delivery system may be configured to deliver leach solution to a lift or stockpile at a level beneath the top surface.

In various embodiments, a system 400 for recovery of metal values may also comprise a PLS collection system. A PLS collection system may be disposed at the bottom of the leach stockpile and configured to collect PLS flowing out of the leach stockpile. Various systems for the collection of PLS at the base of a leach stockpile, such as a leach pad 411 constructed with a liner 414, PLS drainage system 415, and drainage layer 416 as described elsewhere herein, will be well known to a person of ordinary skill and are within the scope of the present disclosure. A PLS collection system in accordance with various embodiments is configured to collect pregnant leach solution flowing out from the leach stockpile and to deliver it to a metal recovery operation, such as a solution extraction plant.

In various embodiments, a system 400 for recovery of metal values from a leach stockpile further comprises a leach solution drainage measure system disposed in the leach stockpile. In various embodiments, the leach solution drainage system comprises a plurality of drainage measures 421, such as a plurality of wick drains. The leach solution drainage system may be configured to facilitate leach solution transfer across zones of low solution permeability 422. The plurality of drainage measures may be configured and/or placed in the leach stockpile in a manner that facilitates leach solution transfer between different lifts in a leach stockpile, such as a first lift and a second lift. In various embodiments, the drainage measure system may be configured to facilitate leach solution transfer to the bottom lift of a stockpile from a distant portion of the stockpile, such as a top or upper lift. For example, a plurality of wick drains may be disposed substantially vertically in the leach stockpile and configured to extend from a location at or near the top surface of the leach stockpile at the upper end of each wick drain into the bottom lift of the leach stockpile at the lower end of each wick drain.

In various embodiments, the lower end of each drainage measure 421 may be located near or adjacent to a portion of the PLS collection system, such as a rock drainage layer 416 overlaying a PLS drainage system 415 comprising HDPE drainage pipe used to collect PLS. However, in accordance with various embodiments of the present disclosure, the drainage measures of a system 400 for recovery of metal values from a leach stockpile are not physically connected to the leach solution delivery system 417 or to the PLS drainage system 415.

In various embodiments, a drainage measure system may comprise a plurality of drainage measures of any type and in any combination of configurations and/or orientations. For example, a system may comprise a plurality of drainage measures 421 that are wick drains disposed at regular intervals throughout the heap and oriented substantially vertically, extending from the top surface of the heap into the bottom lift. In accordance with various embodiments, a system may comprise a plurality of wick drains 421, as described above, in combination with side slope drains 425 disposed in one or more side slopes of the heap. In still other embodiments, a system may comprise drainage measures placed between lifts, such as perforated drainage piping that may be disposed between lifts to facilitate leach solution transfer across a lift interface. The drainage measures of a system in accordance with various embodiments may be placed in the heap during construction of the heap, following construction of the heap, or a combination thereof Likewise, the drainage measures of a system may be placed following identification of regions of poor leach solution flow through the heap or systematically throughout the heap, or both. Any combination of drainage measures, installed in a leach stockpile at any point in construction of the stockpile or performance of a leach operation, and placed in a heap in any manner that facilitates leach solution transfer through the heap, is within the scope of the present disclosure.

Referring again to FIGS. 1 and 2, process of metal value recovery 100 and process for providing improved leach solution drainage 200 may each comprise continued leaching and collection of PLS 60. Continued leaching and collection of leach solution 60 for each process may comprise continued application of leach solution to a lift or heap following placement of a drainage measure or a drainage measure system. In accordance with various embodiments and as described above with respect to processes 100 and 200, placement of one or more drainage measures, or a drainage measure system, may improve leach solution flow through the stockpile and improve recovery of metal value from the stockpile material in the PLS collected from the heap. PLS collected during continued leaching and collection of PLS 60 may be forwarded for metal value recovery, for example, by solution extraction, precipitation, direct electrowinning, carbon adsorption, ion exchange, or the like.

It is believed that the disclosure set forth above encompasses at least one distinct invention with independent utility. While the invention has been disclosed in the exemplary forms, the specific embodiments thereof as disclosed and illustrated herein are not to be considered in a limiting sense as numerous variations are possible. Equivalent changes, modifications and variations of various embodiments, materials, compositions and methods may be made within the scope of the present disclosure, with substantially similar results. The subject matter of the inventions includes all novel and non-obvious combinations and subcombinations of the various elements, features, functions and/or properties disclosed herein and their equivalents.

The method and system described herein may be implemented to facilitate recovery of metal-bearing leach solution from a leach stockpile. Benefits, other advantages, and solutions to problems have been described herein with regard to specific embodiments. However, the benefits, advantages, solutions to problems, and any element or combination of elements that may cause any benefit, advantage, or solution to occur or become more pronounced are not to be construed as critical, required, or essential features or elements of any or all the claims of the invention. Many changes and modifications within the scope of the instant invention may be made without departing from the spirit thereof, and the invention includes all such modifications. Corresponding structures, materials, acts, and equivalents of all elements in the claims below are intended to include any structure, material, or acts for performing the functions in combination with other claim elements as specifically claimed. The scope of the invention should be determined by the appended claims and their legal equivalents, rather than by the examples given above. 

What is claimed is:
 1. A process comprising: identifying a zone of low solution permeability in a leach stockpile; placing a drainage measure in the zone of low solution permeability, wherein the drainage measure comprises a proximal terminus and a distal terminus, and wherein the drainage measure is disposed to place the proximal terminus of the drainage measure on a first side of the zone of low solution permeability and the distal terminus of the drainage measure on an opposite side of the zone of low solution permeability.
 2. The process of claim 1, wherein the drainage measure comprises a non-tubular configuration.
 3. The process of claim 1, wherein the drainage measure is physically separate from a leach solution distribution system.
 4. The process of claim 1, wherein the zone of low solution permeability is identified by at least one of identifying a zone of saturation, identifying a zone of increased material density, and performing core penetration testing.
 5. The process of claim 1, wherein the drainage measure is placed in the leach stockpile following leaching of at least a portion of the leach stockpile.
 6. The process of claim 1, wherein placing a drainage measure in the zone of low solution permeability reduces a hydraulic pressure of the leach solution in the leach stockpile.
 7. A process for producing enhanced leach solution drainage in a leach stockpile comprising: delivering a leach solution to a leach stockpile with a leach solution delivery system; applying the leach solution to at least a portion of the leach stockpile; and installing a drainage measure in a leach stockpile; wherein the drainage measure is selected from a group consisting of: wick drains, pipe drains, perforated pipe drains, sheet drains, strip drains, chimney drains, combination drains, drain holes, and pumps; wherein the drainage measure is physically separate from the leach solution delivery system; and wherein the drainage measure is physically separate from a leach solution collection system.
 8. The process of claim 7, further comprising applying the leach solution to at least a portion of the leach stockpile to produce a partially leached stockpile and installing the drainage measure in the partially leached stockpile.
 9. The process of claim 7, wherein installation of the drainage measure decreases a moisture content of a first region of the leach stockpile adjacent to a first portion of the drainage measure.
 10. The process of claim 7, wherein installation of the drainage measure produces solution transfer from a first region of the leach stockpile to a second region of the leach stockpile.
 11. The process of claim 10, wherein the first region has a higher moisture content than the second region.
 12. The process of claim 11, wherein the first region and the second region are separated by a zone of low solution permeability.
 13. The process of claim 12, wherein solution transfer to the second region produces increased leaching of metal values from a metal-bearing stockpile material in the second region.
 14. The process of claim 7, further comprising installing a system of drainage measures in the leach stockpile.
 15. The process of claim 14, wherein the system of drainage measures comprises a plurality of wick drains installed substantially vertically in the leach stockpile and wherein the plurality of wick drains are arranged in a predetermined configuration across the leach stockpile based on hydraulic properties of a stockpile material.
 16. The process of claim 15, wherein the plurality of wick drains are installed in an order based on identification of at least one of a zone of saturation or a zone of low solution permeability in the leach stockpile, and wherein the order comprises preferentially placing a wick drain at the at least one identified zone.
 17. A system for recovery of metal values from a leach stockpile comprising: a leach stockpile comprising a plurality of stockpile lifts; a leach solution; a leach solution delivery system coupled to the leach solution and configured to deliver the leach solution to the leach stockpile; a leach solution drainage system disposed in the leach stockpile and configured to facilitate leach solution transfer across zones of decreased leach solution permeability; and a leach solution collection system disposed at the bottom of the leach stockpile and configured to collect pregnant leach solution flowing out of the leach stockpile.
 18. The system of claim 17, wherein the leach solution drainage system comprises a plurality of wick drains.
 19. The system of claim 18, wherein at least one of the plurality of wick drains is configured to facilitate leach solution transfer between a first stockpile lift and a second stockpile lift.
 20. The system of claim 18, wherein the plurality of wick drains are disposed substantially vertically in the leach stockpile and wherein each of the plurality of wick drains is configured to extend from a top surface of the leach stockpile into a bottom lift of the leach stockpile. 